As the need for protecting sensitive information which is transmitted over radio communication systems increases, better ways of protecting radio signals from eavesdroppers, becomes more of a concern for individual radio users. In communication devices where protection of voice/data messages is important, a system like the Motorola Digital Voice Protection System can be added to individual radios. The Digital Voice Protection System is an encryption system that converts an analog communication signal into a digital bit stream and then scrambles (encrypts) the digital bit stream with a technique to which only the sender and authorized receivers are given "keys" which allow the signals to be decrypted. If an eavesdropper tries to listen to the conversations on this type of system, the encrypted messages will be able to be received by the eavesdropper, but the messages will sound like pseudorandom noise unless the eavesdropper has the proper key to decrypt the message.
Security concerns in recent years have pushed the state of the art in radio communications to the point that today some communication devices now have multiple key and/or multiple encryption algorithm capabilities (e.g., DES-XL.TM. and DVP-XL.TM., both trademarks of Motorola, Inc.). These communication devices transmit an unencrypted key ID field prior to transmitting the encrypted message in order to inform any receiving radios as to the encryption selected for the particular transmission. The receiving radios then automatically select the encryption to use in order to decrypt the incoming messages and can also by having transmit hangtime capabilities transmit back to the originating radio with the newly selected encryption.
The above mentioned radios unfortunately only give radios the capability of using multiple encryptions. When a radio user wants to originate a new transmission using a new encryption from those found in his radio, he has to manually select the new encryption. A need exists for a radio which can dynamically change the encryption used in encrypting a message sent by the radio on a transmission per transmission basis, thereby offering an even higher standard of security for radio users. A need also exists for a receiver which can predetermine the encryption that will be used by radios in transmitting future transmissions.